Various electric circuits have a protection device incorporated therein in order to protect electric/electronic apparatuses and/or electric/electronic parts, or electric/electronic circuits incorporated therein when a current larger than the rated current flows and/or when a voltage larger than the rated voltage is applied.
As such a protection device, a so-called fusing resistor is known that is a protection device comprising a thermal fuse and a resistive body wherein the resistive body is supplied with a current in an abnormal state so that the resistive body generates heat, the heat activates the thermal fuse (Patent Document 1).
It is also proposed as another protection device to connect a bimetal switch and a positive temperature coefficient (PTC) component in parallel for use (Patent Document 2). In such a protection device, when overcurrent conditions are established, a bimetal portion of the bimetal switch achieves a high temperature so that the contact points become apart from each other and opened, allowing the current to turn to the PTC component. As a result, the PTC component trips to achieve the high-temperature/high resistance state by the overcurrent, substantially cutting off the current flowing through the PTC component.